I'd be interested in the reasons for coming back to the Rezound as well.
I just switched to the SIII yesterday after my Rezound bit the dust. I was in Vancouver and the battery died on me while on a ferry and never came back. Charged it over night, tried a new battery, took it to Verizon, various other tricks and it never came back. Wouldn't even try to boot up. So, I guess never let your Rezound battery die in Canada?
Anyway, Verizon offered a refurbed Rezound but I decided to change it up with the SIII.
So far, the phone is really nice but I can say without a doubt, the Rezound matched and even exceeded it in some areas. The Rez was just as fast, smoother in transitions, and IMO had a better, brighter and sharper screen. I also prefer Sense.
The SIII so far has a better battery (though I did just get it) and I like the size and thickness better than the Rezound. I thought the SIII would feel flimsy but it's seems to be pretty well built despite it's weight. I also thought the larger size would be an issue but the SIII is overall just a slight bit bigger than the Rez. The camera seems to be on par with the Rez but I have not really had a chance to test it out more in depth.
The biggest difference is the UI. I really like Sense but I'm sure I will get used to the Samsung UI. Just takes a little time.
I was also worried about the signal after reading all the bad stories about Samsung phones in general. I'm in the Seattle area and so far, I've been getting a strong 4G signall with no drops to 3G or 1x. Calls have been very clear and the people on the other end say I sound fine. In contrast, my Rez was constantly and randomly dropping to 1x. It was actually becoming quite irritating. The first 6 months with the Rez were fine with strong 3g/4g signals but all of a sudden the 1x drop kept happening. Seemed to be a common problem.
Anyway, I loved the Rezound but it's death provided me a opportunity for a change. So far, I have no regrets.